I beleive the NewCastle is the faster of the 2 processors
I have the Clawhammer but i have it set to 2.2 (same as newcastle)
The newcastle is also newer.
If they are the same price i would get the newcastle.
BUT i would wait and get a socket 939 mobo with a 3800+ i beleive
its only 2.4ghz (which is still more than the 3200&3400, and the same as the FX-51&FX-53)
It is the fastest processor AMD makes. It runs dual channel unlike the 3200&3400 and it uses Unbuffered ram which is MUCH cheaper than registered and MUCH faster.
but if you can't wait...3200+newcastle is the way to go